"RPG" is a bit of a misnomer, as it is a backronym of the Russian name for the weapon. Arguably, they're just rockets, although you can distinguish between other rocket weapons (M1 Bazooka, Panzerschrek) in which the warhead fits inside the tube and is loaded from the back. Since the warhead is outside the pipe, this allows it to be larger, granting more penetrating power and more freedom for warhead design. However, as a rocket, they are self propelled for the first five seconds of flight.

A recoilless rifle would ideally be rifled and recoilless gun would not, but recoilless rifle is often used for both. The propellant is expended entirely inside the firing chamber of the gun, and is vented backwards to counter the recoil of the bullet. Additionally, the rounds resemble bullets more than they resemble fin-stabilized rockets.